Why does Vi take long time to run motor

[sobansair]

hi 

i am using a VFD to run motor by using feedback PID.

i am measuring frequency with NI 9401 and converting into rpm.

i am using NI 9263 for voltage output.

but the issue is when i run vi it doesn't run motor immediately,it takes long time to run motor or sometime  doesn't run motor

i am attaching my VI below.

vfd is by PARKER 690 + 

[GerdW]

Hi sabansair,

but the issue is when i run vi it doesn't run motor immediately,it takes long time to run motor or sometime  doesn't run motor

- you are using those DAQAssistents: while it is not completely wrong it doesn't help a lot. Better use plain DAQmx functions…

- your P gain is rather small, so the reaction of the PID will also be small to control errors

- is there a reason to divide measured RPM and setpoint by 150?

- does the PID output the expected values?

- are there any errors from your DAQAssistents?

- there is no (fixed) timing in your loop…

[sobansair]

hi Sir

1 i have tried with DAQmx functions but my vi doesn't start a motor.i have attached vi below.

2 yes when i set P gain high using Daq assistant motor starts in 10sec. but i want to start motor instantly.

3-yes once motor start PID gives desired results

4- yes at small P value error message appeared to increase buffer size.but once set higher Pvalue=4 no error message appear and pid works well.

6-  1v=150rpm so to convert rpm to voltage i divide it by 150

my requirement is once i give setpoint value.motor  should start instantly. kindly check my daqmx VI too. 

[GerdW]

Hi sobansair,

1. Are there any error messages (any DAQmx errors?) when "the motor doesn't start? In the "untitled" VI you divide 60 by the counter value, but in the "Engine head" VI you multiply counter by 60: is this difference important and intended? (Why are you using a Realtime-Wait function in one of those VIs? Do they run on RT systems?)

2. Did you analyze the PID output value? Is it the PID delaying your motor start or is something else responsible?

3. Ok, fine.

4. PID P gain is NOT related to any DAQmx buffer size. Not at all!

6. That's why you should use more comments in your code. I prefer to use the label of those constants to place related information…